Shown under construction, One World Trade Center may not officially reach its design height of 1,776 ft, depending on how its redesigned spire is assessed by the Council on Tall Buildings and Urban Habitat. Courtesy of Wikimedia Commons/Utahredrock
A redesign of the spire at the top of One World Trade Center may prevent it from officially reaching the symbolic height of 1,776 ft.
June 5, 2012—One World Trade Center is already the tallest building in New York, having reached 1,271 ft in April, but its ranking as the tallest building in the western hemisphere when completed in 2013 is up in the air.
The tallest building designation hinges on whether the 408 ft spire that tops the building can be counted in One World Trade Center’s height. With the spire, the structure will measure a symbolic 1,776 ft, outranking Chicago’s 1,451 ft Willis Tower and 1,389 ft Trump International Hotel and Tower. If the spire is not counted, One World Trade Center will measure 1,368 ft tall, relegated to the third tallest in North America behind Chicago’s two giants.
The spire comprises a base and seven stacked sections that provide space for broadcast equipment, as well as an eighth section that contains a beacon. Steel cables anchored to a ring at the spire’s base will support the structure, and additional equipment, lighting, and window washing rigs could be attached to the ring.
To lend visual weight to the spire, integrate it into the building’s design, and shield it from the elements, architect David Childs, FAIA, a consulting partner at Skidmore, Owings & Merrill (SOM), designed a “sculpted cladding” to cover the spire’s exterior. The cladding would be a tapered enclosure, 23 ft in diameter at its widest point, featuring a folded-plate assembly of 2.5-in. thick fiberglass-and-foam interlocking triangular panels. To mitigate wind shear and potential structural fatigue, fin-like strakes would spiral from the base to the tip of the cladding. (See “Final World Trade Center Tower Design is Safe, ‘Green,” and Sculptural,” Civil Engineering, February 2004, pages 13-14, and “Redesigned Freedom Tower Addresses Security Concerns,” Civil Engineering, August 2005, pages 18-19.)
The Port Authority of New York and New Jersey and The Durst Organization, of New York City—the building’s co-owners and developers—expressed concerns about maintaining the cladding. When SOM came back with a maintenance plan that involved positioning a free climber on the spire, mounting winches at the spire’s top, and lifting 2,000 lb panels into place from a staging area on the 9/11 Memorial site, the owners decided to eliminate the cladding. (SOM declined to be interviewed for this article.)
Although eliminating the cladding from the spire will save approximately $20 million in construction costs, Jordan Barowitz, the director of external affairs for Durst, denies that financial considerations played a role in the decision. “The design was changed not because of cost or design but because of an inability to maintain the structure,” he says.
Denuded of its cladding, the spire is a pole of galvanized steel truss work, 6 ft in diameter, intersected by maintenance platforms—a structure that most people would describe as an antenna. And therein lies the risk to One World Trade Center’s ranking and symbolic height. According to the Council on Tall Buildings and Urban Habitat (CTBUH), the official arbiter of tall building designations and rankings, spires count in a building’s height for ranking purposes, antennas do not.
Kevin Brass, the CTBUH’s public affairs manager, explains that the CTBUH makes its determinations on the basis of official, agreed-upon definitions. “We don’t make judgments. We just track the data. Our goal is to be fair and accurate,” he says.
The CTBUH defines a building’s height as the distance from the level of the lowest open-air pedestrian access to the structure’s “architectural top.” The definition specifically includes spires but excludes antennas, flagpoles or other “functional technical equipment.” The spire with cladding would be considered an integral part of the building, and the building’s height would be measured to the spire’s top. If the CTBUH determines that the spire without the architectural cladding is an antenna, the “architectural tip” of the building would be the top of the antenna, but the architectural top would be the roof at 1,368 ft.
The CTBUH will not make a decision until the building is complete. “It’s not unusual for design to change during construction,” Brass notes. “There have already been a couple [of changes to 1 World Trade Center], and there may be more. We will want to get all the data, the drawings, and the statistics, and then the committee will make a decision.”
In making a decision, the committee will consider more than the presence or absence of the architectural cladding, he adds. “We consider whether the spire is part of the design, part of the tower’s form and function, whether it is inherent to the building in the architect’s vision.”
The Durst Organization, meanwhile, gives no credibility to the antenna argument. “The spire will be lit with LEDs and have a beacon at the top that will serve as a lighthouse,” Barowitz says. “The spire is an architectural element of the building.”
New Yorkers will soon be able to judge for themselves whether the building topper is merely an antenna or qualifies as an architectural element. The Durst Organization reports that the spire is being fabricated now and will be assembled this summer.
Architect Childs has been vocal in expressing his opinion on the issue, issuing a statement in which he said he is “disappointed that a decision has been made to remove the sculptural enclosure at the top of 1 World Trade Center.” He has called the resulting structure an “exposed antenna.”